Two-color QCD at imaginary chemical potential and its impact on real chemical potential

We study properties of two-color QCD at imaginary chemical potential (μ) from the viewpoint of the Roberge-Weiss periodicity, the charge conjugation, and the pseudoreality. At μ=±iπT/2, where T is temperature, the system is symmetric under the combination of the charge conjugation C and the Z₂ transformation. The symmetry, called CZ₂ symmetry, is preserved at lower T but spontaneously broken at higher T. The Polyakov-loop extended Nambu-Jona-Lasinio model has the same properties as two-color QCD for CZ₂ symmetry and the pseudoreality. The nontrivial correlation between the chiral restoration and the deconfinement are investigated by introducing the entanglement vertex in the Polyakov-loop extended Nambu-Jona-Lasinio model. The order of CZ₂ symmetry breaking at the Roberge-Weiss end point is second order when the correlation is weak, but becomes first order when the correlation is strong. We also investigate the impact of the correlation on the phase diagram at real μ.